2 Great Stone Bridge in ChinaHistory of Bridge Development100 B.C. Romans2,104 years ago700 A.D. Asia1,304 years agoClapper BridgeRoman Arch BridgeTree trunkStoneArch designevenly distributesstressesNatural concretemade from mudand strawClapper Bridges employed all over the world, most notably in England. Originally, tree logs used, but they tended to rot. Stones were better, but difficult to maneuver. The Romans developed highways that connected the empire. Bridges helped them do this.Great Stone Bridge in ChinaLow bridgeShallow archAllows boatsand water to passthrough

3 History of Bridge Development19001920Truss BridgesMechanics of DesignWood2000Suspension BridgesUse of steel in suspending cablesPrestressed ConcreteSteel

4 Basic ConceptsSpan - the distance between two bridge supports, whether they are columns, towers or the wall of a canyon.Force -CompressionTensionCompression –Tension -Concrete has good compressive strength, but extremely weak tensile strength. What about steel cables?

5 Basic Concepts Beam - a rigid, usually horizontal, structural elementPierPier - a vertical supporting structure, such as a pillarCantilever - a projecting structure supported only at one end, like a shelf bracket or a diving boardLoad - weight on a structure

6 Types of Bridges Basic Types: Truss Bridge Beam Bridge Arch BridgeSuspension BridgeFloating BridgeFloatingTrussBeamArchSuspensionThe type of bridge used depends on the obstacle. The main feature that controls the bridge type is the size of the obstacle.

7 Truss Bridge Typical Span Lengths 40m - 500m World's LongestPont de QuebecTotal Length863mCenter Span549mA Matsuo Example2nd Mameyaki BridgeTypical 40m to 500mAll beams in a truss bridge are straight. Trusses are comprised of many small beams that together can support a large amount of weight and span great distances.

8 Types of Bridges Beam BridgeConsists of a horizontal beam supported at each end by piers. The weight of the beam pushes straight down on the piers. The farther apart its piers, the weaker the beam becomes. This is why beam bridges rarely span more than 250 feet.

9 Types of Bridges Beam Bridge ForcesWhen something pushes down on the beam, the beam bends. Its top edge is pushed together, and its bottom edge is pulled apart.

10 Types of Bridges Arch BridgesThe arch has great natural strength. Thousands of years ago, Romans built arches out of stone. Today, most arch bridges are made of steel or concrete, and they can span up to 800 feet.

11 Types of Bridges Arch Bridges ForcesThe arch is squeezed together, and this squeezing force is carried outward along the curve to the supports at each end. The supports, called abutments, push back on the arch and prevent the ends of the arch from spreading apart.

12 Types of Bridges Suspension BridgesThis kind of bridges can span 2,000 to 7,000 feet -- way farther than any other type of bridge! Most suspension bridges have a truss system beneath the roadway to resist bending and twisting.

13 Types of Bridges Suspension Bridges ForcesIn all suspension bridges, the roadway hangs from massive steel cables, which are draped over two towers and secured into solid concrete blocks, called anchorages, on both ends of the bridge. The cars push down on the roadway, but because the roadway is suspended, the cables transfer the load into compression in the two towers. The two towers support most of the bridge's weight.

14 Types of Bridges Floating BridgePontoon bridges are supported by floating pontoons with sufficient buoyancy to support the bridge and dynamic loads.While pontoon bridges are usually temporary structures, some are used for long periods of time.Permanent floating bridges are useful for traversing features lacking strong bedrock for traditional piers.Such bridges can require a section that is elevated, or can be raised or removed, to allow ships to pass.

17 Bridge Engineering SummaryTo design a bridge like you need to take into account all the forces acting on it:The friction of the earth on every partThe strength of the ground pushing up the supportsThe resistance of the ground to the pull of the cablesThe dead weight and all vehicle loadsThen there is the drag and lift produced by wind and waterThe turbulence as fluids pass the towersNeed to use appropriate materials and structural shapes in the cheapest way, yet maintaining a certain degree of safety.To account for natural disasters, engineers design bridges with a factor of safety: usually around 3 or 4.

18 Case Study: Tacoma Narrows FailureThe first Tacoma Narrows suspension bridge collapsed due to wind-induced vibrations on Nov. 7, The bridge over engineered it to withstand hurricane winds, but the wind that day was only 40 mph… what happened!?